Circuit arrangement for coupling a tuned circuit with a tube



CIRCUIT ARRANGEMENT FOR COUPLING A TUNED CIRCUIT WITH A TUBE July 14, 1936. a. D. H. TELL-EGEN Filed. March 5 1934 Fig .1

flll -illillnllll INVENTOR BERNARDUS D.//. TELLEGE/V ATTORNEY Patented July 14, 1936 UNITED STATES PATENT OFFICE CIRCUIT ARRANGEMENT FOR COUPLING A TUNED CIRCUIT WITH A TUBE Application March 5, 1934, Serial No. 714,024 In Germany May 13, 1933 3 Claims.

This invention relates to circuit arrangements for coupling a tuned circuit with a thermionic vacuum tube.

With the usual high frequency amplifying arrangements the tuned circuits are often directly connected to the anode or the grid of the amplifying tube. The desired frequency is obtained by tuning the variable condenser. Since the amplification and the selectivity depend on the ratio between the internal tube resistance and the impedance of the circuit the amplification factor increases at higher frequencies (consequently at a smaller value of the tuning condenser). On the contrary the selectivity will decrease with an increasing frequency.

The invention has for its purpose to couple the circuit to the tube in such a manner that the coupling becomes looser at an increasing frequency. Owing to this, the circuit at an increasing frequency is influenced to a lower extent by the internal resistance of the tube due to which the effect referred to is compensated.

The invention is carried out by coupling the circuit with the tube through a small variable condenser. This condenser is so constructed that it increases or decreases exactly in accordance with the tuning condenser. Advantageously both condensers are coupled in a constrained manner. For higher frequencies the coupling condenser will consequently have a small value, so that the circuit is coupled less closely with the tube, whilst at low frequencies (consequently when the coupling condenser has a large value) the coupling will be closer.

The coupling according to the invention offers the additional advantage that due to the looser coupling of the circuit at high frequencies the influence of capacity variations of the tube which may result both from interchanging tubes and from sound strength modification by means of a tube, on the circuit decreases which is particularly advantageous for apparatus having a plurality of circuits and single knob control.

Furthermore the tubes have a smaller tendency to self-oscillate on account of the smaller ampliflcation at higher frequencies.

The invention will be more clearly understood by reference to the accompanying drawing representing, by way of example, some forms of construction thereof.

In Fig. 1 the tuned circuit CL is interposed in the anode circuit of a tube. The tuning condenser C, which may advantageously have a maximum value of 400 mmF, is mechanically .coupled with the coupling condenser Ck whose maximum value amounts, for instance, to mrnF.

In Fig. 2 the tune-d circuit is inserted in the grid circuit of a tube.

In Fig. 3 the tuned circuit CL is coupled with coupling condensers Ck both with the anode of the preceding and with the grid of the next tube. The tuning condenser C is mechanically coupled with both coupling condensers Ck.

What I claim is:

1. An electrical system comprising a pair of thermionic discharge deviceis, a tuned circuit interposed between said devices, said tuned circuit including a variable condenser, a variable coupling condenser interposed between said tuned circuit and the device preceding that circuit and a second variable coupling condenser V interposed between said tuned circuit and the device which follows said tuned circuit, said variable coupling condensers and the variable tuning condenser being connected for uni-control.

2. Apparatus according to claim 1 in which means are provided for simultaneously varying said tunable coupling condensers to decrease the coupling between said tuned circuit and the preceding and following devices when the tunable condenser in the tuned circuit is varied to increase the frequency to which said tuned circuit is tuned.

3. The combination with a pair of electron discharge tube amplifiers provided with grid and anode electrodes, of a tunable circuit including a variable impedance, a variable coupling condenser connected between the tunable circuit and the anode of one of the amplifier, a second variable coupling condenser connected between the tunable circuit and the grid of the other amplifier, and means interconnecting both coupling condensers with said variable impedance of the tunable circuit for simultaneous operation.

BERNARDUS D. H. TELLEGEN. 

